The response of cell cultures of pulmonary endothelium to injury will be studied. Cells from the bovine pulmonary artery and from smaller vessels within the lung will be injured in vitro by infectious agents (viral and bacterial) by treatment with lysosomal proteases from polymorphonuclear leukocytes and by treatment with mediators of inflammation. Mediators that will be tested are the following: histamine, bradykinin, activated Hageman factor, antigen-antibody complexes and chemotactic polypeptides. The onset, extent and consequences of endothelial injury will be assessed morphologically by light microscopy and by transmission and scanning electron microscopy. The localization of antibodies to Factor VIII, basement membrane collagen and fibronectin will be carried out using immunofluorescence microscopy and immunoelectron microscopy. The growth response and the level of protein synthesis will be determined. The type of collagen synthesized by pulmonary endothelium will be assessed and quantitated during the course of injury. We will study the relationship between injury and the secretion of fibronectin and Factor VIII by endothelial cells. We will also study the relationship between injury and granulocyte adherence to the endothelium. Light and electron microscopic studies will correlate morphology with biochemical, immunological and granulocyte adherence studies.